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Yr 2 - Clinical Pathology > Pathogen-Antibiotic Matching 1 > Flashcards

Pathogen-Antibiotic Matching 1 Flashcards

1
Q

How do gram positive bacteria stain? Why?

A
  • Purple
  • Due to thick peptidoglycan cell wall
    • This takes up purple stain
  • Due to this thick cell wall, it does not need an additional outer membrane
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2
Q

How do gram negative bacteria stain? Why?

A
  • Pink
  • Thinner peptidoglycan cell wall BUT has an additional outer membrane
    • This membrane stops the crystal violet stain from penetrating the cell wall and hence does not become purple in response to the crystal violet stain
  • Also due to the lack of peptidoglycan, meaning the stain cannot be retained
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3
Q

Describe cocci shape

A

Round - can be in pairs, chains or groups

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4
Q

Describe bacilli shape

A

Rods - groups, chains

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5
Q

gram positive/negative cocci/bacilli

A
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6
Q

Examples of classifications

A
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7
Q

What classification is S. aureus and S. epidermis?

A

Gram positive cocci

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8
Q

What classification is Strep pneumoniae and Strep pyogenese?

A

Gram positive cocci

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9
Q

What classification is clostridium difficile?

A

Gram positive bacilli

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10
Q

What classification is Listeria?

A

Gram-positive bacilli

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11
Q

What classification is Neisseria meningitides and Neisseria gonorrhoea?

A

Gram negative cocci

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12
Q

What classification is E. coli?

A

Gram negative bacilli

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13
Q

What classification is salmonella?

A

gram negative bacilli

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14
Q

What is the most common mechanism of antibiotics?

A
  • Antibiotics that interfere with cell wall synthesis
    • ​Prevent rigid cell wall from being assembled
  • This includes the beta-lactams
    • Prevent peptidoglycan from being incorporated into the cell wall
    • Bacteria fall apart
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15
Q

What are the 2 main classes of antibiotics that inhibit cell wall synthesis?

A
  • Beta-lactams:
    • Penicillins: amoxicillin, penicillin V
    • Cephalosporin: cefuroxime
    • Carbapenem: meropenem
  • Glycopeptides: vancomycin
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16
Q

Antibiotics can also target protein synthesis (translation), causing bacteria death. What are 4 important examples of these antibiotics?

A
  • Tetracyclin (doxycycline)
  • Macrolides (erythromycin)
  • Chloramphenicol
  • Aminoglycosides (gentamycin)
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17
Q

Antibiotics can also target RNA synthesis. Which antibiotic targets this?

A

Rifampicin

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18
Q

Antibiotics also target DNA replication. What are 3 examples of these?

A
  • Quinolones (Ciprofloxacin)
  • Metronidazole
  • Anti-folates (folate is key in DNA replication)
    • Trimethoprim
    • Sulfa drugs
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19
Q

What are the 4 mechanisms by which antibiotics kill bacteria?

A
  1. Inhibit cell wall synthesis
  2. Inhibit protein synthesis/translation
  3. Inhibit RNA synthesis
  4. Inhibit DNA replication

All these targets are specific to bacteria - don’t harm human cell

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20
Q

What is the zone of inhibition? What is it used to measure?

A
  • The Zone of inhibition is a circular area around the spot of the antibiotic in which the bacteria colonies do not grow
    • Bigger zone = more effective antibiotic
  • Can be used to measure the susceptibility of the bacteria to wards the antibiotic.
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21
Q

What are the 4 mechanisms of drug resistance? What are examples for each?

A
  • Drug inactivation or modification
    • ​Bacteria produce enzyme that destroys antibiotic
      • Staph aureus –> penicillinase
      • E. coli –> carbapenemase
  • Alteration of target or binding site
    • ​Target of antibiotic changes shape so antibiotic can no longer bind and interfere with it
      • Staph aureus –> alteration of penicillin binding protein
  • Alteration of metabolic pathway
    • ​Sulfa resistant bacteria can use pre-formed folic acid (instead of having to rely on making some)
  • Reduced drug accumulation
    • Bacteria can express a drug pump in their cell membrane so antibiotics are pumped out of cell and back into environment and do not accumulate in cell
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22
Q

What type of antibiotic is Amoxicillin? Mechanism?

A
  • Beta-lactam antibiotic, penicillin type
  • Broad-spectrum activity against different types of infections caused by both Gram-positive and Gram-negative bacteria
  • Mechanism: Inhibits cell wall synthesis
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23
Q

What is Amoxicillin used for?

A

ENT, respiratory and urinary infections

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24
Q

How can bacteria can resistance to Amoxicillin? What has been developed in response to this resistance?

A
  • Produce B-lactamase enzymes which break down B-lactams
  • Developed Co-Amoxiclav in response to this:
    • Amoxicillin + clavulanic acid
      • Clavulanic acid inhibits b-lactamase to help stop bacteria breaking down Amoxicillin
  • Co-Amoxiclav is therefore useful against B-lactamase producers
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25
Q

What is Tazocin a combination of?

A

Works same way as Co-Amoxiclav:

  • Piperacillin (antibiotic) + Tazobactam (inhibits the action of bacterial β-lactamases)
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26
Q

What type of antibiotic is Flucloxacillin? Mechanism?

A
  • B-lactam antibiotic
  • Only active vs gram positive bacteria
  • Mechanism: inhibits cell wall synthesis
    • Bidns to penicillin binding protein
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27
Q

What is Flucloxacillin only active against?

A

Gram positive bacteria

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28
Q

What is Flucloxacillin mainly used to treat?

A

Staph aureus infections –> binds to penicillin binding protein

29
Q

What is MRSA?

A
  • Methicillin resistant S. aureus
  • Has mutation in penicillin binding protein – resistance to fluclox
30
Q

Can beta lactams be used to treat MRSA? What needs to be used instead?

A
  • No due to mutation in penicillin binding protein
  • Have to use other antibiotic class such as Vancomycin
31
Q

Compare the spectrum of activity of:

  • Penicillin
  • Cephalosporins
  • Carbapenems
A

Penicillin (Amoxicillin) < Cephalosporins (Cefuroxime) < Carbapenems (Meropenem)

e.g. Carbapenems are really broad spectrum

32
Q

Clinical Case:

  • 73 year old male is admitted with fever, cough shortness of breath and purulent sputum.
  • He is confused, has a blood pressure of 80/55 and a respiration rate over 30
  • What is diagnosis?
  • What treatment would you start? Why?
A
  • Pneumonia
  • Co-amoxiclav + clarithromycin
    • This is a systemic combination for community acquired pneumonia for someone who is very unwell
    • Broad spectrum as not yet sure what pathogen is causing it
33
Q

What score is used to calculate the severity of community-acquired pneumonia and, therefore, treatment?

A
  • CURB-65 score
    • Confusion
    • Urea <7
    • Respiration >30
    • BP <90/60
    • Age >65
34
Q

What antibiotics are given to low risk pneumonia?

A

Amoxicillin

35
Q

What antibiotics are given to high risk pneumonia?

A

Co-amox + clarithromycin

36
Q
  • What shape and gram-stain is this pathogen?
  • If this pathogen is causing pneumonia, what is it likely to be?
  • What antibiotic is used to treat this?
A
  • Gram-positive cocci
  • Streptococcus pneumoniae
    • This is the most common cause of community acquired pneumonia
  • Narrow spectrum penicillin (as Strep pneumo is sensitive to this)
    • Fewer side effects compared to co-amox and clarithromycin
37
Q

What pathogen is the most common cause of community acquired pneumonia?

A

Streptococcus pneumoniae

38
Q

Which pathogen tends to cause hospital acquired pneumonia?

A

Klebsiella and other gram negatives

39
Q

What antibiotic is used to treat pneumonia caused by Strep pneumoniae?

A

Penicillin

40
Q

What is the relationship between side effects and the spectrum of an antibiotic?

A

Broad spectrum = more side effects

41
Q

Clinical Case 1 Part 2

Your previous patient continues to be treated with co-amoxiclav and clarithromycin for 10 days (not switched to Amoxicillin). His chest improves. On day 10 he develops abdominal pain and green, watery diarrhoea.

  • What is your diagnosis?
  • How do you treat this?
A
  • Clostridium difficile infection
    • Gram-positive bacilli
    • Common complication of broad spectrum antibiotic use
  • Stop current antibiotics and start oral vancomycin
    • As pneumonia has been cured
    • Oral vancomycin is very targeted to C. difficile as stays in gut
42
Q

What is a common side effect of broad spectrum antibiotic use? Why?

A
  • Clostridium difficile infection
  • Gut flora contains many bacteria which are all in competition with each other
  • Broad spectrum antibiotics destroy a majority of species allowing a few to overgrow (Clostridium difficile)
    • Clositridium difficile is a toxin producer –> colitis
43
Q

Which broad spectrum antibiotics are most likely to lead to C. difficile infection?

A

Ciprofloxacin, cefuroxime, co-amoxiclav in elderly patients in particular

44
Q

Clinical Case 2

A 20 year old woman presents to her GP with pain on urinating and frequent urination. She does not have a fever or any loin pain.

  • What is your diagnosis?
A
  • Lower urinary tract infection
45
Q

How do lower UTIs present?

A
  • Dysuria
  • Frequency
  • Sometimes pain when pressing bladder
46
Q

What do lower UTIs involve the infection of?

A

Urethra and bladder

47
Q

If bacteria migrate up the ureter and into the kidney from a lower UTI, this can lead to an upper UTI. How would patients present?

A
  • Fever
  • Loin pain
  • Tachycardia
  • Low blood pressure

This is a much more severe infection and can lead to sepsis

48
Q

How would an upper UTI be treated?

A
  • Broad spectrum antibiotics to start –> IV Cefuroxime
    • Until you know which pathogen is causing it
49
Q

How would a lower UTI be treated?

A
  • Narrow spectrum antibiotic –> Nitrofurantoin, trimethoprim, pivmecillinam
50
Q

What are the most common bacteria to cause UTIs?

A
  • Gram negative bacillus:
    • E. coli (most common)
    • Proteus, Klebsiella
  • Gram positive coccus:
    • Staphylococcus saprophyticus
51
Q

Who is Staphylococcus saprophyticus most likely to cause UTIs in?

A

Young sexually active females

52
Q

Clinical Case 3

At the end of fresher’s week a 22 year old student starts feeling unwell. He develops a fever and becomes increasingly confused over the day. His friends ring an ambulance.

On admission he has neck stiffness and struggles with bright light (photophobia).

A cerebrospinal fluid sample shows the following.

  • What is classification of pathogen
  • What is the diagnosis?
  • What pathogen has caused this?
  • What is treatment for this?
A
  • Round shaped, pairs –> diplococci
  • Pink –> gram negative
  • Meningitis caused Neisseria meningitides
    • ​Gram negative cocci
  • Treatment: IV broad spectrum antibiotic –> IV Ceftriaxone
53
Q

How is meningitis treated?

A
  • Broad spectrum antibiotic at first –> IV Ceftriaxone
  • Narrow spectrum after pathogen has been found
54
Q

Which bacteria typically causes meningitis in:

  • Children and young adults?
  • Elderly patients and neonates?
A
  • N. meningitides
  • Streptococcus pneumoniae
  • Previously also Haemophilus influenza (now vaccinated)
55
Q

If a patient with meningitis also presents with a non-blanching rash and was systemically unwell with low blood pressure and tachycardia, what would this be?

A

Meningococcal septicaemia:

  • a bloodstream infection caused by Neisseria meningitidis
  • the bacteria enter the bloodstream and multiply, damaging the walls of the blood vessels. This causes bleeding into the skin and organs.
56
Q

Define sepsis

A
  • Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection - a body’s response to an infection injures its own tissues and organs
  • Organ dysfunction = change in SOFA score ≥2
57
Q

What does sepsis cause?

A
  • Drop in O2 conc
  • Impaired coagulation with fall in platelets
  • Liver dysfunction with rise in bilirubin
  • Impairment of circulatory system with a fall in BP
  • Mental impairment with a fall in the Glasgow Coma Scale
  • Renal impairment with a rise in creatinine and a fall in urine output
58
Q

Abbreviated SOFA score for sepsis:

A
  • Low BP
  • High respiratory rate
  • Altered mental state
59
Q

Managment of SEPSIS –> BUFALO

A
  • Blood cultures: 2 sets
  • Urine output: Patient catherised to measure urine output
  • Fluids: 500ml IV saline over 15 minutes. Aim 30ml/kg in 1 hour.
  • Antibiotics: As per suspected infection
  • Lactate: Arterial blood gas for lactate and pH
  • Oxygen: 15 l/min via reservoir face mask
60
Q

What fluids are given in suspected sepsis? Why?

A
  • 500ml IV saline over 15 minutes
    • Aim 30 ml/kg in 1 hour
  • The body needs extra fluids to help keep the blood pressure from dropping dangerously low, causing shock
    • The fluid is called isotonic, as it does not change the size of the cells.
61
Q

Clinical Case 4

A 50 year old man sustains a skin scrape while working in the garden. Over the next few days develops the following picture and he has a fever:

A

Cellulitis

62
Q

What is cellulitis? How does it present?

A
  • Skin and soft tissue infection
    • Bacterial
    • The bacteria can infect the deeper layers of your skin if it’s broken – for example, because of an insect bite or cut, or if it’s cracked and dry.
  • The affected skin appears swollen and red and is typically painful and warm to the touch.
63
Q

What bacteria is cellulitis caused by? How is it treated?

A
  • Gram positive cocci e.g. Staph aureus and Step pyogenes
  • Treated with Flucloxacillin
64
Q

What is necrotising fascitis? Which bacteria typically causes it? What is the treatment?

A
  • A severe skin and soft tissue infection caused by a polymicrobial mix, but usually involving Streptococcus pyogenes.
  • Treatment:
    • Debridement: removing all infected tissue
    • Meropenem + clindamycin
      • Meropenem: carbapenem-type antibiotic
      • Clindamycin: is active against Gram-positive cocci, including streptococci and penicillin-resistant staphylococci, and many anaerobes.
65
Q

Clinical Case 5

A 25 year old PWID (person who injects drugs) is admitted with a 2 week history of fever, night sweats and shortness of breath.

He has a heart murmur on auscultation.

  • What is your top differential?
A
  • Infective endocarditis
    • Bacteria has been introduced straight into bloodstream via needle
  • N.B. PWID are also at high risk of blood borne viruses (e.g. HIV, hep B, hep C) so also need to screen for these
66
Q

What is infective endocarditis? What pathogens typically cause it? What is treatment?

A
  • Infection of heart valves
  • Many possible pathogens but most common:
    • Staph aureus
    • Streptococci
  • ~6 weeks IV antibiotics depending on bacteria
67
Q

Why are PWID most at risk of infective endocarditis caused by bacteria that live on your skin?

A

As needle penetrates skin, it takes bacteria along with it into the blood which can then settle on your valves: Staph aureus and Streptococci

68
Q

Which antibiotics are the most well tolerated and safe in pregnancy?

A

Beta lactams: penicillins and cephalosporins

69
Q

Which antibiotics should be avoided/limited use in pregnancy? What damage can each of these do?

A
  • Quinolones (ciprofloxacin) – damage to cartilage
  • Trimethoprim – folic acid antagonist
    • Most important to avoid in 1st trimester
  • Tetracyclins – deposits and stains bones/teeth

Yr 2 - Clinical Pathology (80 decks)

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